Sound should fit Japanese Buzzard but is somewhat similar to Eastern Black-eared Kite.
Curious to know too what's in the background but the recording has a lot of background noise (wind, lens-zooming in and out)
Most of these background singers have been puzzling me all trip

Thank you Anon, that's the confirmation i was hoping for. In Europe Buzzards are hard enough -sometimes- to separate from similar species, and i have no experience with them in Japan. Thanks again for helping to build my knowledge of Japanese birds. regards, Gerben